foo.c: In function 'main':
foo.c:15:2: warning: implicit declaration of function 'gets_s'; did you mean 'gets'? [-Wimplicit-function-declaration]
  gets_s(s1); gets_s(s2);
  ^~~~~~
  gets
/tmp/ccM3HGgM.o: In function `main':
foo.c:(.text.startup+0x64): undefined reference to `gets_s'
foo.c:(.text.startup+0x6e): undefined reference to `gets_s'
collect2: error: ld returned 1 exit status

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